To achieve this, you could set AssignmentRule to 'Anchor First' for all the type A orders(which you want to serve first). You should create many 2-order routes and then consolidate. For the routes, you could set MaxOrderCount to 2. Once you get several individual routes, consolidate those to keep the required number of routes based on other constraints you might have.

I think this should work. If not, please let us know and we would be happy to help.